Robotic cleaning devices, such as robotic vacuum cleaners, are known in the state of the art. One such robotic cleaning device is disclosed in U.S. Pat. No. 5,369,347, which reference is incorporated herein. This known device comprises a housing having an overall shape of a circular block. For driving the device, the device is provided with one driving wheel and two support wheels, which support wheels are arranged at diametrical opposite sides of the device. For steering the device, the driving wheel is pivoted around a vertical axis.
Such a known device can be operated in the following manner. When the device moves forwards, the driving wheel is oriented in parallel with the support wheels. If, for example, the device hits an obstacle on the left side thereof, the driving wheel is pivoted 90° to the right, whereby the device is brought to a complete halt before it will start to rotate. The rotation will be to the right and, because the support wheels are arranged on a diameter of the circular device, around a central axis between the support wheels. Furthermore, due to the round shape of the device, the obstacle will not obstruct the rotation of the device. When the device has turned 90°, the driving wheel is pivoted 90° to the left it will again be parallel with the support wheels. The device will start to move forward and is allowed to travel a small distance. Then, the driving wheel is pivoted 90° to the left, wherein the device again is caused to stop before it starts to turn left around the central axis.
After the device has turned 90° left, the driving wheel is pivoted back to being parallel with the support wheels and the device will again travel forward in the original direction. A problem with this known robotic cleaning device is that it is time and energy consuming to steer the device around obstacles, for example table legs or chair legs, which are common in normal home environments. This is especially a problem with battery operated robotic cleaning devices, since the batteries thereof often have to be reloaded or recharged, which extends the cleaning time even more.
It is of course also possible to rotate the driving wheel less then 90° when the device hits an obstacle. However, since the device in that case will not turn around a central axis, a problem with this way of operation is that the device will not move clear of the obstacle, but will be pushed backwards by the obstacle during the rotation or will even get stuck.